The baritone saxophone uses a single reed, a thin shaped strip of case which vibrates to produce sound. The back of the reed is flat, and is placed against the mouthpiece. All single reeds are of similar shape, but vary in size to fit the instrument's mouthpiece. Baritone saxophone reeds may look identical to each other, but may vary in thickness which affects the sound and playability of the instrument. This is generally measured on a scale of 1 to 5 from softest to hardest. This is not a standardized scale and reed strengths vary by manufacturer.